Changed market requirements regarding the power spectrum of batteries of coke ovens have led to the construction again nowadays of chamber ovens in which the crude gas produced during the coking process is not provided for producing sulfur, tar, benzene, etc., but is directly combusted in the coking chamber (upper oven) and the sole flues (lower oven) arranged below the latter in order to provide the required process heat. The completely combusted gas is then either conducted away into the atmosphere (NR—Non Recovery) or heat is extracted from said gas in a downstream process step, for example in order to produce superheated steam (HR—Heat Recovery). In both cases, these NR/HR ovens substantially differ in the manner of their heating from indirectly heated horizontal chamber ovens in which the heating system and the coking chamber are decoupled materially from each other.
Modern NR/HR ovens are constructed from silica material. Older types of oven are based on fireclay material. Insulating materials are additionally installed in the ceiling region, floor region and in the side regions of the ovens for heat insulation purposes.
The NR/HR ovens of newer type are distinguished in that two-stage combustion and therefore two-stage heating take place in them. Some of the crude gas which is produced is incompletely combusted (primary combustion) in the upper oven directly above the coal mass in the coking space (primary heating space) by addition of primary air. Heat is transmitted here directly by gas and solid-state radiating processes.
The partially combusted gas is then conducted out of the upper oven via downwardly directed downcomer channels located in the lateral oven walls below the oven bottom into the lower oven and is completely combusted there in sole flues (heating flues) by repeated addition of secondary air (secondary combustion) before said gas is evacuated into an exhaust gas collecting channel as a result of the negative pressure operating mode. In the case of known oven structures, at least one and up to 10 downcomer channels are accommodated in an oven wall. The sole flues can be arranged here horizontally, in meandering form or in parallel and coupled to one another in the direction of flow in the form of an approximately U-shaped deflection. By means of the secondary combustion in the sole flues, the complete combustion of the gas which was previously only incompletely combusted during the primary combustion in the upper oven takes place in the lower oven. The heat thus produced in the lower oven by secondary combustion is indirectly transmitted to the coal in the coking chamber located above said lower oven, analogously to the heat transmission mechanisms which are also known, for example, from the conventional horizontal chamber technique.
However, as practice has shown, the time and the quantity of the addition of secondary air have a decisive effect on the uniformity of the heating in the lower oven, especially in the sole flues. The undefined addition of secondary air in the lower oven can immediately lead to high process temperatures above 1600° C. and therefore to melting processes of the construction material of the oven and to destruction of the oven structure. This then inevitably results in failure of coke production since the ovens first of all have to be repaired in a complicated manner in a procedure using heat before they can be filled again.
There is therefore a need for improved geometry for the sole flues, which ensures, with high process efficiency, homogeneous surface heating of the coal charge in the sole flue coupled below the silica support layer, with the unsteady production of combustion gas being taken into consideration, wherein local superheating on the brickwork surface and exhaust gas cooling processes are avoided at the same time. The following are of high importance here in the longitudinal direction of the oven: 1. the positions of the downcomer channels in the lateral oven walls, 2. the structural configuration of the reversing point between outer and inner sole flue, 3. the positions of the secondary air supply openings in the floor of the sole flues, and 4. the regulation of the partial quantities of gas in the downcomer channels.
U.S. Pat. No. 6,596,128 B2 relates to a method for reducing the volumetric flows flowing in a sole exhaust gas system for a coke oven at least during the initial coking process after filling of the coke oven with coal. The method comprises providing a channel system between a first coke oven with a first coking chamber and a second coke oven with a second coking chamber in order to conduct at least some of the gas from a gas space in the first coking chamber to the second coke oven, as a result of which the gas flow rate in the first sole exhaust gas system of the first coke oven is reduced. The reduction in the gas flow rates in the sole exhaust gas system has a positive effect on the product throughput, the service life of the coke oven and the environmental control of volatile emissions from coke ovens.
DE 10 2007 061502 B4 discloses a device for supplying and regulating secondary air from the secondary air channels into the flue gas channels of horizontal coke chamber ovens. The flue gas channels are located here under the coke oven chamber floor on which the coking process takes place. The flue gas channels serve for combusting partially combusted coking gases from the coke oven chamber. The partially combusted coking gases are combusted with secondary air, as a result of which the coke cake is also heated from below for uniform coking. The secondary air comes from the secondary air channels which are connected to the outside air and to the flue gas channels. Regulating elements which can control the airflow into the flue gas channels are installed in the connecting channels between the flue gas channels and the secondary air channels. This enables more uniform heating and distribution of heat in coke chamber ovens.
DE 10 2009 015270 A1 discloses a method and a device for evening out the burn-up characteristics and for reducing the thermal NOx emissions of a coking plant on the basis of the non-recovery process or the heat-recovery process using a multiplicity of ovens. The ovens each have an oven space delimited by doors and side walls for a bed of coal or a compacted coal cake, and an empty space located above said oven chamber, devices for extracting the exhaust gas from the empty space, devices for supplying fresh air into the empty space, a system of sole flues for conducting exhaust gas or secondary feed air, which system is at least partially integrated into the floor under the oven space, wherein some of the exhaust gas produced in the oven is returned into the oven space via openings or channels for the combustion process of the oven.
CN 2505478Y relates to a coke oven, in particular to a heat recovery coke oven, wherein a smoke flue is installed in the lower part of the furnace flue, and wherein a control device is mounted at the inlet of the smoke flue.
CN 2500682Y relates to a coke oven with a lateral infeed, wherein a combustion chamber is located under the floor plate of the coking chamber, said combustion chamber consisting of four arcuate combustion chambers arranged in the longitudinal direction, and wherein an air channel which is connected to the combustion chamber is located on the floor of the combustion chambers in the longitudinal direction. In this case, two combustion chambers each form a unit and are separated by a partition, wherein overflow openings for the coal gas are located at the ends of the partitions of each combustion chamber unit.
CN 1358822A relates to a heat-recovery tamping-type coke oven which has an arched oven ceiling, a control device for the primary airflow, a control device for the secondary supply of air, a rising furnace flue in the oven wall, a furnace flue leading downward, a four-arch oven floor, and a two-plane structure of the oven doors.
FIG. 1 according to DE 10 2009 015270 A1 shows a single deflection at each of the transitions of the two outer sole flues into the two inner sole flues. Furthermore, the outer downcomer channels are at comparatively large distances from the respectively adjacent outside edge of the oven. In the two outer sole channels over the length of the oven, the cross sections of the downcomer outlet openings and of the secondary air inlet openings are not located at a common level. This geometry takes into consideration deflection cross sections of 0.1 to 1.1 m2. This arrangement with a single deflection of the exhaust gas into the inner sole flues, lack of gas regulation in the downcomer channels and very large distances between the outer downcomer channels and the respectively adjacent outside edge of the oven results in a plurality of disadvantages: the coal charge is non-uniformly heated from below and local superheating occurs associated with a possible destruction of the brickwork materials in the region of the transition of the exhaust gas flow from the outer sole flue into the inner sole flue. This is the case in particular whenever the use limit of the customarily used silica material of approx. 1873 K is locally exceeded. Furthermore, as a consequence of the large distances of the outer downcomer channels from the respectively adjacent outside edge of the oven, the end sides of the coal cake are heated only inadequately, and therefore an insufficient quality of the coke is produced.
The combination of the geometry shown in FIG. 1 of DE 10 2009 015270 A1 with the single-flame design according to U.S. Pat. No. 6,596,128 B2 (FIG. 5) does not lead to an advantageous homogeneous heating of the oven from below either. The adaptation of the known single-flame design according to U.S. Pat. No. 6,596,128 B2 to the known geometry of the sole flue according to DE 10 2009 015270 A1 can cause local superheating associated with tertiary combustion in the exhaust gas system if, for example, as a consequence of a manual operating error, the cross section of the air regulating flap is too greatly throttled or too low a negative pressure is present in the exhaust gas system. In this solution, it is also of disadvantage if, as a consequence of too large a free flow cross section of the air regulating flap or as a consequence of too high a negative pressure in the exhaust gas system, an inadequately high quantity of air is sucked into the sole flues such that the resulting exhaust gas temperature at the heat exchanger located downstream undershoots the nominal value, which is associated in turn with a lower production of steam, i.e. lower process efficiency. At the same time, the cooling of the sole flues leads to an undesirable reduction in the process efficiency of the following charge since this process efficiency is determined by the heat which is generated by crude gas combustion during the coking of the precursor charge and is stored in the brickwork. The throughflow length of the outer and inner sole flues between the coke side and machine side of the oven is customarily 9 to 20 m in each case. Furthermore, the two-sided single-flame solution according to U.S. Pat. No. 6,596,128 B2 therefore has the disadvantage that, in the case of typical flame lengths of in each case only approx. 1.5 to 3.5 m, said flame lengths do not reach into the inner regions of the sole flue and do not generate any additional secondary combustion heat portions there, and therefore the center of the coal charge located thereabove in the coking chamber is frequently characterized by zones of reduced coke quality or even with uncoked coal. If the single-flame solution of U.S. Pat. No. 6,596,128 B2 is applied to the geometry of the application DE 10 2009 015270 A1, a nonuniform temperature level with a large temperature difference between the extreme values of approx. 350 K is produced in the flow profile of the sole flue assembled from the outer part and the inner part. As a consequence of an operating error in the heating setting in the outer sole flue, the maximum use limit of the silica material may then be exceeded, which is synonymous with destruction of the brickwork. At the same time, this setting leads to an undesirable reduction of the exhaust gas temperature with reduced production of steam in the heat exchanger.